This invention relates to an optical router with optical control.
In a telephone switching office, it is conventional to observe the condition of an optical fiber line used for telephone communication by use of a test instrument that includes an optical time domain reflectometer (OTDR) unit. As is well known, the OTDR unit has an optical I/O port that is optically coupled to the fiber line under test, and the OTDR unit launches pulses of optical energy into the line under test and measures the intensity with which optical energy is returned by way of the I/O port. In order to allow a single OTDR unit to observe multiple optical fiber lines, an optical router is interposed between the optical I/O port on the OTDR and the optical fiber lines. The router has an upstream port that is coupled to the optical I/O port of the OTDR unit and has multiple downstream ports and includes an optical switch for optically coupling its upstream port with any selected downstream port. The OTDR unit is electrically connected to the router for supplying commands to the router for controlling the state of the switch. The router responds to a command by causing the switch to connect the upstream port of the router to a selected downstream port.
The OTDR unit of the test instrument is controlled from an automated/manual control system that provides electrical control signals to the OTDR unit and receives electrical response messages from the OTDR unit.
In order to allow the OTDR unit to observe more optical fiber lines than the router has downstream ports, one or more of the downstream ports of the router may be connected to the upstream port of a second level router having downstream ports connected to respective optical fiber lines. The electrical control signals for controlling operation of the second level router are supplied by the operator interface, which receives response messages from the second level switch.
It will be seen that by adding routers in a star or cascade arrangement, a single OTDR unit can be used to observe a large number of optical fiber lines.
A disadvantage of the arrangement described above is that it is necessary to provide electrical connections not only between the operator interface and the OTDR unit, but also between the operator interface and each router (other than the highest level router). This is inconvenient because the routers that are lower in the hierarchy might be at a considerable distance from the OTDR unit.